JPH07158435A - Exhaust pipe for internal combustion engine - Google Patents

Abstract

PURPOSE:To reduce the manufacturing cost of an exhaust pipe of double pipe structure for an internal combustion engine. CONSTITUTION:An exhaust pipe for an internal combustion engine is provided with an outer pipe 1 with a flange 4 welded at least to one end part thereof, an inner pipe 2 disposed almost concentrically with a specified clearance 5 to the outer pipe 1, and a clearance keeping member 6 disposed between the outer pipe 1 and the inner pipe 2 at least at one end part in order to keep the specified clearance 5. In this case, the flange 4 and the clearance keeping member 6 are simultaneously welded to the outer pipe 1 by single welding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust pipe of an internal combustion engine having a double pipe structure.

[0002]

2. Description of the Related Art In recent years, exhaust gas regulations have become stricter, and it is necessary to activate a catalytic converter early when an engine is started. As an exhaust pipe for this purpose, Japanese Utility Model Laid-Open No. 5-19522 discloses an exhaust pipe having a double-pipe structure including an outer pipe that maintains strength and a thin inner pipe. In this exhaust pipe, an air layer is formed between the inner pipe and the outer pipe as a heat insulating layer, and the heat capacity of the thin inner pipe is small. It becomes possible to lead to the catalytic converter, and the catalyst can be brought to the activation temperature early.

In the exhaust pipe of the above-mentioned double pipe structure, the inner pipe and the outer pipe which spread like a trumpet are firmly welded at one end, and the above-mentioned air layer is maintained and the both pipes are maintained at the other end. In order to allow the difference in thermal expansion, a ring member which is welded to only one of the tubes and is slidable with respect to the other tube is arranged between the tubes.

[0004]

In the above-mentioned prior art, in addition to the welding of the mounting flanges at both ends of the outer pipe, the welding of both pipes at one end and the one pipe at the other end described above. If the ring member is welded, there are many welding points, the manufacturing time becomes long, and the manufacturing cost may increase.

Therefore, an object of the present invention is to provide an exhaust pipe of an internal combustion engine having a double pipe structure, the manufacturing cost of which can be reduced.

[0006]

An exhaust pipe of an internal combustion engine according to the present invention has an outer pipe having a flange welded to at least one end thereof, and an inner pipe arranged substantially concentrically with the outer pipe with a predetermined gap. An exhaust pipe of an internal combustion engine, comprising: a gap maintaining member disposed between the outer pipe and the inner pipe at least at one end to maintain the predetermined gap; The member and the member are simultaneously welded to the outer pipe by one welding.

[0007]

In the above-described exhaust pipe of the internal combustion engine, since the gap maintaining member for maintaining the predetermined gap between the outer pipe and the inner pipe is simultaneously welded to the outer pipe by the single welding together with the flange, Manufacturing time is reduced.

[0008]

1 is a partial sectional view showing a first embodiment of an exhaust pipe of an internal combustion engine according to the present invention. In the figure, 1 is an outer tube and 2 is an inner tube. At both ends of the outer tube 1,
A first flange 3 on the exhaust manifold side and a second flange 4 on the catalytic converter side are attached. As shown in FIG. 3, which is an enlarged P arrow view of FIG. 1, the second flange 4 has an elliptical shape, and bolt holes 100 for connection with the catalytic converter case are provided on both sides in the longitudinal direction. ing. In order to maintain the strength of the entire exhaust pipe, the outer pipe 1
It has a thickness of about 1.5 to 2 mm.

The inner tube 2 has a relatively thin thickness of about 0.6 to 1 mm, and when it is in a straight line, it is
Expanded portions 2a, 2 expanded to be approximately equal to the inner diameter of the outer tube 1.
b is formed, and the end portion 2c on the first flange 3 side is expanded into a trumpet shape and inserted into the outer tube 1 in a linear state. After that, the first flange side end portion 2c is welded to the outer pipe 1, and by bending the outer pipe 1 into a desired shape, the expanded pipe portion 2a,
The inner tube 2 abutting by 2b is also bent into the same shape. The expanded portions 2a and 2b of the inner tube 2 are positioned so as to avoid the curved portions thereof, and as shown in FIG. 2 which is an enlarged AA sectional view of FIG. It functions to maintain a predetermined gap 5 between the pipes 1 and 2 in the vicinity.

Exhaust gas flows in from the first flange 3 side and is discharged from the second flange 4 side. At this time, since the end portion 2c of the inner pipe 2 on the first flange 3 side is welded to the outer pipe 1 over the entire circumference, the exhaust gas does not flow into the predetermined gap 5 between the pipes 1 and 2. It surely passes through the inner pipe 2.

Especially at the time of cold start of the engine, since the catalyst temperature of the catalytic converter is low and sufficient exhaust gas purification performance cannot be realized, it is necessary to set the activation temperature to an early activation temperature. The exhaust pipe having the double pipe structure as in this embodiment is the outer pipe 1
The predetermined gap 5 formed between the inner pipe 2 and the inner pipe 2 forms an air layer as a heat insulating layer, and the inner pipe 2 has a small thickness, so that the heat capacity thereof is small. The exhaust gas temperature can be led to the catalytic converter without being lowered so much that the catalyst can be warmed up early.

In the exhaust pipe of the double pipe structure used in this way, both pipes 1 and 1 are caused by the temperature difference between the outer pipe 1 and the inner pipe 2.
Between the two, a difference in thermal expansion particularly in the axial direction occurs. Inner tube 2
In the expanded portions 2a, 2b of the pipe, since the length from the end of the first flange 3 on which the pipes 1 and 2 are fixed is relatively short, the difference in thermal expansion between the pipes 1 and 2 generated there. Is not so large, and wear when the expanded pipe portions 2a and 2b slide on the inner surface of the outer pipe 1 is very small, but a similar expanded pipe portion is formed on the inner pipe 2 at the end portion on the second flange 4 side. Then,
Since the pipes 1 and 2 are greatly slid to cause considerable wear and the mechanical strength of the exhaust pipe as a whole is lowered, generally, FIG. 3 which is an enlarged P arrow view of FIG. As shown in the figure, in order to maintain the predetermined gap 5 at this portion, a ring member 6 formed of a wire mesh having a small sliding resistance is inserted between the pipes 1 and 2.

The ring member 6 is fixed to only one of the pipes, thereby allowing relatively large sliding between the other pipe and the other pipe with little wear. As shown in FIG. 5, which is an enlarged cross-sectional view of the conventional second flange 4, when this ring member 6 is fixed to the inner pipe 2 by spot welding, it is formed by a wire mesh that is very easy to melt. Since the sliding surface 6a of the ring member 6 is formed with a recess in the spot welded portion, the above-mentioned sliding becomes unstable, and the inner tube 2 has a thinner wall thickness at that portion. Is reduced.

Further, as compared with the normal single pipe structure exhaust pipe, if this spot welding is performed in addition to the welding at the first flange side end portion 2c of the inner pipe 2, the number of welding spots increases, Therefore, the manufacturing time becomes longer and the manufacturing cost increases. In this embodiment, as shown in FIG. 4, which is an enlarged cross-sectional view of the second flange 4 side in FIG. 1, a ring member 6 is arranged on the back side of the welded portion of the second flange 4 to the outer pipe 1, and this welding is performed. The ring 6 is joined to the outer tube 1 by the back bead generated at this time.

As a result, the spot welding described above is omitted, and the manufacturing time can be shortened and the manufacturing cost can be reduced accordingly. Further, such a back bead has a relatively low temperature, the ring member 6 formed by the wire mesh is not so much melt-damaged, and naturally, the melt-damage of the inner pipe 2 is prevented.

When such an exhaust pipe having a double pipe structure is actually attached to an internal combustion engine and used, a relatively large vibration may occur. In this embodiment, since the expanded pipe portions 2a and 2b of the inner pipe 2 are in close contact with the outer pipe 1, both pipes vibrate similarly at these portions, and at the end of the second flange 4 side. , Both pipes vibrate relatively freely, but the ring 6 formed by the wire mesh prevents the inner pipe 2 and the outer pipe 1 from colliding with each other in order to prevent the collision of the two pipes 1 and 2. Noise is not generated.

In this embodiment, as described above, the ring member 6 is formed by the back bead when the second flange 4 is welded to the outer pipe 1.
The back bead is not exposed in the predetermined gap 5 because it is joined. As in the conventional case shown in FIG. 5, when such a back bead is exposed, the back bead and the inner tube 2 may collide with each other due to the deformation of the ring member 6 during vibration, which may cause abnormal noise. However, this embodiment can solve this problem at the same time.

FIG. 6 is a partial cross-sectional view showing a second embodiment of the exhaust pipe of an internal combustion engine according to the present invention. The difference from the first embodiment is that the expanded portions 2a, 2b of the inner pipe 2 are omitted. Instead, the gap maintaining member 7 formed of a wire mesh is used. As shown in FIG. 7, which is an enlarged BB cross-sectional view of FIG.
Of the four members 7a, which are located in a radial direction with some of the parts omitted,
It is formed of 7b, 7c and 7d. With such a gap maintaining member 7, the predetermined gap 5 can be maintained as with the ring member 6 described above, and the collision between the pipes 1 and 2 during vibration can be prevented.

When the predetermined gap 5 is maintained with such a wire mesh member, they are easily deformed when the above-mentioned outer pipe 1 and inner pipe 2 are bent,
It is necessary to fill the predetermined gap 5 with sand or the like. The gap maintaining member 7 described above is not ring-shaped but has a shape in which a part thereof is omitted in order to enable sand removal after bending. Since the ring member 6 at the end of the second flange 4 is inserted after this sand removal and welded in the same manner as in the first embodiment, the same effect as in the first embodiment can be obtained. it can.

By the way, in the case where an oxygen sensor for detecting the oxygen concentration in the exhaust gas is attached to the exhaust pipe of such a double pipe structure, this attachment position is advantageous for early warm-up of the oxygen sensor itself. The end portion on the first flange 3 side upstream of the exhaust gas is selected. Since the general mounting structure is unstable in strength when directly welded to the thin inner tube 2, as shown in FIG.
Is welded to the outer tube 1 having a sufficient strength, and the detecting portion 10b penetrates the inner tube 2 and projects into the inside. In such mounting, the oxygen sensor 1 is provided in order to make it difficult for exhaust gas to flow into the predetermined gap 5.
When the gap between the detection unit 10b of 0 and the through hole of the inner pipe 2 is narrowed or a seal member or the like is arranged in this gap, the temperature difference between the outer pipe 1 and the inner pipe 2 due to the predetermined gap 5 is caused. Due to the difference in thermal expansion between the two, the oxygen sensor 10 may be bent and damaged.

In the third embodiment of the exhaust pipe of the internal combustion engine according to the present invention, as shown in FIG. 9 which is an enlarged sectional view of the end portion on the first flange 3 side, the inner pipe 2 is compared with the first embodiment.
The contact portion of the trumpet-shaped expanded portion 2c with the outer tube 1 is made relatively long, and the oxygen sensor 1 is configured to penetrate the contact portion.
0 is welded to the outer tube 1. Thereby,
In this part, there is no gap between the outer tube 1 and the inner tube 2,
Since the temperatures of the both are almost equal and no difference in thermal expansion occurs, generation of bending stress in the oxygen sensor 10 is prevented.

Further, in the fourth embodiment of the exhaust pipe of the internal combustion engine according to the present invention, as shown in FIG. 10 which is an enlarged cross-sectional view of the end portion of the first flange 3 side, as compared with the first embodiment, The welding position of the trumpet-shaped expanded portion 2c of the tube 2 to the outer tube 1 is deep, and the oxygen sensor 10 is attached to the portion where the outer tube 1 exists independently. This mounting structure is used for the oxygen sensor 1 due to the difference in thermal expansion between the tubes 1 and 2.
In addition to preventing damage to the oxygen sensor 10, the heat capacity of the portion to which the oxygen sensor 10 is attached is smaller than that of the third embodiment because only the outer tube 1 is provided. It is advantageous for own early warm-up.

FIG. 11 is an enlarged sectional view of an end portion of the exhaust pipe of the internal combustion engine according to the present invention on the first flange 3 side showing a fifth embodiment. The difference from the first embodiment is that the inner pipe 2'is not provided with a trumpet-shaped expanded portion 2c at the end portion on the first flange 3 side, and only this portion 2'c has the same thickness as the outer pipe 1. The first flange 3 is welded to its end. Further, a trumpet-shaped expanded portion 1'a is formed at the end portion of the outer pipe 1'on the side of the first flange 3, and this expanded portion 1'a is attached to the above-mentioned portion 2'c of the inner pipe 2 at the first flange 3 '. Are sufficiently separated from each other and welded, and a predetermined gap 5 is formed between the outer pipe 1'and the inner pipe 2 '. The oxygen sensor 10 is adapted to be welded to the aforementioned portion 2'c of the inner pipe 2 '.

The attachment structure of the oxygen sensor 10 has the same effect as that of the fourth embodiment, and since the joint welding portion of both pipes 1 and 2 is exposed, this welding can be performed very easily. It is possible.

In all the examples, the ring member 6 formed from the wire mesh used as the gap maintaining member at the end portion on the second flange side does not limit the present invention, and its material has a small sliding resistance. It is possible to use other materials, and the manufacturing cost reduction that is the object of the present invention can be sufficiently achieved even if the material is divided into radial shapes as used in the middle of the exhaust pipe.

[0026]

As described above, according to the exhaust pipe of the internal combustion engine of the present invention, the outer pipe having the flange welded to at least one end thereof and the inner pipe arranged substantially concentrically with the outer pipe with a predetermined gap therebetween. A pipe, and a gap maintaining member arranged at least at one end between the outer pipe and the inner pipe to maintain a predetermined gap,
In the exhaust pipe of the internal combustion engine including the above, since the flange and the gap maintaining member are simultaneously welded to the outer pipe by one welding, the manufacturing time can be shortened and the cost can be reduced accordingly. .

[Brief description of drawings]

FIG. 1 is a partial sectional view showing a first embodiment of an exhaust pipe of an internal combustion engine according to the present invention.

FIG. 2 is an enlarged AA sectional view of FIG.

3 is an enlarged P arrow view of FIG. 1. FIG.

FIG. 4 is an enlarged cross-sectional view of a second flange side end portion of FIG. 1.

FIG. 5 is an enlarged sectional view of a conventional second flange side end portion.

FIG. 6 is a partial sectional view showing a second embodiment of the exhaust pipe of the internal combustion engine according to the present invention.

FIG. 7 is an enlarged BB sectional view of FIG.

FIG. 8 is a cross-sectional view showing a conventional oxygen sensor mounting structure at an end portion on the first flange side.

FIG. 9 is a cross-sectional view at the end portion on the first flange side showing the third embodiment of the exhaust pipe of the internal combustion engine according to the present invention.

FIG. 10 is a sectional view of an end portion of a first flange side showing an exhaust pipe of an internal combustion engine according to a fourth embodiment of the present invention.

FIG. 11 is a sectional view of an end portion of a first flange side showing an exhaust pipe of an internal combustion engine according to a fifth embodiment of the present invention.

[Explanation of symbols]

 1 ... Outer tube 2 ... Inner tube 3 ... 1st flange 4 ... 2nd flange 5 ... Predetermined gap 6 ... Ring member 7 ... Gap maintenance member 10 ... Oxygen sensor

Claims (1)

[Claims] 1. An outer pipe having a flange welded to at least one end, an inner pipe arranged substantially concentrically with the outer pipe with a predetermined gap, and at least the one end for maintaining the predetermined gap. In an exhaust pipe of an internal combustion engine, comprising: a gap maintaining member disposed between the outer pipe and the inner pipe, the flange and the gap maintaining member are simultaneously welded to the outer pipe by one welding. An exhaust pipe of an internal combustion engine, characterized in that